JPH0221188B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a call loop control circuit for a public telephone.

Generally, public telephones are equipped with a battery for operating a relay that closes a call loop. That is, the battery is charged by the power source of the central office exchange, and the voltage of the battery is supplied to a relay control circuit, which operates the relay to close the call loop. As described above, conventional public telephones use a battery as a power source for a relay control circuit for operating a relay, but since a battery is used as a power source, there are various disadvantages as described below.

(1) Before installing the battery in a public telephone, it is necessary to charge the battery using a charger. Furthermore, even if the public telephone is charged in advance, it will self-discharge if a long period of time elapses before the public telephone is installed, and it is necessary to inspect it immediately before installing it and charge it again.

(2) Since batteries have a large amount of energy, if the circuit pattern on the printed board is short-circuited due to a defect in the control circuit or an incorrect operation, there is a risk of burning out the circuit pattern. Furthermore, if such an accident occurs and the battery voltage drops, the battery must be recharged each time. Furthermore, if a short circuit accident occurs as described above, self-heating may shorten the life of the battery, and the gas generated inside may cause liquid leakage, which may damage other electrical or mechanical parts. There is also a risk of corrosion.

(3) Since the lifespan of the battery is relatively short, it is necessary to periodically inspect it, and it is also necessary to consider the structure of the phone so that it can be easily charged.

As described above, using a battery as an operating power source for a relay control circuit has various disadvantages, and there is room for improvement in the future.

This invention was made in view of the above points,
The voltage obtained from the central office exchange through the telephone line is stored in a capacitor, and the charging voltage of this capacitor is used as a power source.The charging voltage is compared with a predetermined reference level and the charging voltage exceeds the specified value. To provide a call loop control circuit for a public telephone that eliminates the need for charging a battery using a charger and prevents unstable operation due to low voltage below a specified value by closing the call loop only when the call loop is closed. The purpose is to

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows the overall configuration of an embodiment of the present invention. A portion 1 surrounded by a dashed line is a public telephone, which is connected to a central office exchange 2 via telephone lines l ₁ and l ₂ . Ru. This public telephone 1 includes a telephone circuit 11 connected to the telephone lines l ₁ and l ₂ via line terminals a and b, and a first relay contact interposed between the telephone circuit 11 and the line terminal b.
RYS ₁ , a power supply circuit 12 connected to the line terminals a and b, a capacitor 13 connected between the output terminals 12a and 12b of this power supply circuit 12,
The voltage monitoring circuit 14 monitors the voltage across the capacitor 13, a relay control circuit 15 operates using the charging voltage of the capacitor 13 as a power source, and a relay RY controlled by the relay control circuit 15. A communication loop is formed by the communication circuit 11, the first relay contact RYS ₁ , and the communication lines l ₁ and l ₂ . Further, although it is preferable to use a latching relay as the relay RY in order to reduce current consumption, it does not necessarily have to be a latching relay. In this embodiment, a case will be explained in which a latching relay is used.

By the way, the configuration of the voltage monitoring circuit 14 and the relay control circuit 15, and the configuration of each of these circuits and the relay
The connection relationship between RY and its second contact RYS ₂ is specifically as shown in FIG. In FIG. 2, the same parts as in FIG. 1 are given the same reference numerals. 21 is a comparator, the charging voltage V _C of the capacitor 13 is input to its negative input terminal, and the constant voltage V ₁ by the Zener diode ZD ₁ and the constant voltage by the Zener diode ZD ₂ are input to the positive input terminal.
Of V ₂ , V ₁ (hereinafter referred to as V _L ) or V ₁ + V ₂ (hereinafter referred to as V L)
_VH ) can be input selectively. 22 is an AND circuit, one input terminal of which is supplied with the output of the comparator 21 via an inverter 23, and the other input terminal of which is supplied with the timing signal S. The above timing signal S is generated when the switch is raised at a public telephone.
Or, it is a general operation signal generated when a coin is inserted by raising the switch. 24 ₁ ,
24 ₂ is a transistor for controlling the operation of relay RY, and the base of transistor 24 ₁ is resistor R ₁
connected to the input terminal of the AND circuit 22 via
The base of the transistor 24 ₂ is connected to the output terminal of the AND circuit 25 via a resistor R ₂ . Further, the collectors of these transistors 24 ₁ and 24 ₂ are connected to coils C ₁ and C ₂ of relay RY. The Zener diode ZD ₁ is connected to the terminal voltage V _C 12 of the capacitor 13 via a resistor R ₃ .
The constant voltage V _L caused by this Zener diode ZD ₁ is set in advance so that the relay control circuit operates stably and the voltage value is sufficient to restore the relay RY.

By the way, one input terminal of the AND circuit 25 is connected to the output terminal of the comparator 21, and the other input terminal is connected to one fixed contact _t1 of the relay contact _RYS2 , and also connected to the capacitor via the resistor _R4 . is connected to the terminal voltage V _C. The relay contact RYS ₂ above is a switching contact, and the relay
When RY is not in operating state, it is on the fixed contact _t1 side,
When the transistor 24 ₁ turns on and voltage is applied to the relay coil C ₁ and the relay RY operates, it switches to the other fixed terminal t ₂ side, and then the transistor 24
₂ turns on and voltage is applied to relay coil C ₂ , which activates the relay.
When RY is restored, it returns to the fixed terminal _t1 side again. Note that the fixed terminal t ₂ is connected to the connection point of the Zener diodes ZD ₁ and ZD ₂ . A relay control unit 30 is connected to the base of the transistor 24 ₂ via a resistor Rr. This relay control section 30 receives the state of the switch 31 and generates an operation signal S when the switch 31 is turned off, and generates a return signal E when the switch 31 is turned on.
It has the function of generating Further, this relay control section 30 is equipped with the following functions.
In other words, a function that detects the inserted coin, enables a call for a time corresponding to the amount of money, and then generates a return signal E when the time corresponding to the amount has elapsed, a function that stores coins according to the call time, a function that returns the remaining balance, etc. It is.

Next, the operation of the present invention configured as described above will be explained. In the initial state, relay RY is not operating, the first contact RYS ₁ is open, and the second contact is open.
RYS ₂ is switched to terminal t ₁ side. A voltage check of the terminal voltage V _C of the capacitor 13 in such a state is performed as follows.

That is, in the above state, comparator 2
A Zener diode ZD ₁ is connected to the positive input terminal of 1,
A constant voltage V _H (V ₁ + V ₂ ) due to ZD ₂ is input, and the terminal voltage V _C of the capacitor 13 is equal to the above constant voltage.
V _H and its magnitude are compared. Here, if V _C >V _H , the output of the comparator 21 becomes a low level (“0”), and the output is inverted by the inverter 23 ₁ and input to one input terminal of the AND circuit 22 . At this time, a timing signal S (high level) is input to the other input terminal of the AND circuit 22, and this timing signal is applied to the transistor
Send to TR ₁ . This turns on transistor TR ₁ , supplies current to relay coil C ₁ , and operates relay RY. Due to the operation of relay RY, the first
The contact RYS ₁ closes to form a communication loop, and the second contact RYS ₂ switches to the terminal t ₂ side and maintains that state. In this way the second contact point
By switching RYS ₂ to the terminal t ₂ side, only the constant voltage V _L from the Zener diode ZD ₁ is input to the positive input terminal of the comparator 21 . When the hook switch 31 is turned on in this state, the relay control section 30 generates a return signal E. This return signal is input to the base of the transistor ₂₄₂ through the resistor Rr. As a result, transistor 24 ₂ is turned on and current is supplied to relay coil C ₂ . Thus, relay RY
is restored, the first contact RYS ₁ is opened to open the communication loop, and the second contact RYS ₂ is switched to the terminal t ₁ side, returning to the initial state.

Next, in the same way as above, the first contact RYS ₁ is closed to form a call loop, and the second contact
A case where a component of the relay control circuit 15 fails while RYS ₂ is switched to the terminal t ₂ side will be explained. By the way, if a failure of this component occurs in, for example, the transistor 24 ₁ , current continues to flow through the relay coil C ₁ , and the electric charge stored in the capacitor 13 is no longer able to supply power to the relay coil C ₁ .
This causes the relay control circuit 15 to have low impedance when viewed from the capacitor 13. Incidentally, when storing coins or returning the balance, the magnet is driven, and even if the transistor that drives the magnet fails, the relay control circuit 15 becomes low impedance in the same manner as described above. When the relay control circuit 15 becomes a low impedance in this way, the charging voltage V _C of the capacitor 13 decreases, and when V _C <V _L , the output of the comparator 21 becomes a high level (“1”). As a result, the AND circuit 25 is turned on, and this time the transistor 24 ₂
turns on, current is supplied to relay coil _C2 , and relay RY is restored. When the relay RY is restored, the first contact RYS ₁ is opened to open the communication loop, and the second contact RYS ₂ is switched to the terminal t ₁ side to return to the initial state.

As is clear from the above operation, when setting the public telephone, the charging voltage V _C of the capacitor 13 is
While the voltage is so small that the control circuit 15 and the relay RY cannot operate stably (V _C <V _H ), the control circuit 15 and the relay RY are not operated. In other words, the charging voltage of the capacitor 13 is
The communication loop will not be closed until the voltage reaches a level that allows for sufficiently stable operation (V _C > V _H ). This makes it possible to reliably prevent unstable operation due to low voltage below the specified value.

Next, when relay RY operates and the call loop is closed, the reference voltage of comparator 21 is
Switches from V _H to V _L , and in this state, the charging voltage V _C of the capacitor 13 decreases due to the above-mentioned reason.
When V _C < V _L , the relay RY is restored and the call loop is opened. By performing such an operation, the inconvenience of continuing to close the communication loop even in the event of a failure is eliminated.

It should be noted that the present invention is not limited to the above-mentioned embodiments, but includes, for example, the configurations of the voltage monitoring circuit 14 and relay control circuit 15, and the configurations of these circuits and relays.
RY, its connection relationship with the second contact RYS ₂ is the third
A configuration as shown in the figure may also be used. In Figure 3, the second
The same parts as in the figure are given the same reference numerals. In the case of this figure 3, the voltage level of V _L is set by the Zener diode ZD ₁ , the voltage level of V _H is set by the Zener diode ZD ₂ , and the terminal t ₁ of the second contact RYS ₂ is connected to the Zener diode ZD ₂ . It is connected to the connection point with the resistor R ₅ , and the terminal t ₂ is connected to the connection point between the Zener diode ZD ₁ and the resistor R ₆ . Here, if V _C > V _H , the output of the comparator 21 becomes "1", the transistor 24 ₁ is turned on, current is supplied to the relay coil C ₁ , and the relay RY is driven, and the first contact RYS ₁
is closed, forming a communication loop, and at the same time, the second contact RYS ₂ is switched to the terminal t ₂ side. In this state, V _C decreases due to component failure, etc., and when V _C < V _L ,
The output of the comparator 21 becomes "0", which is inverted by the inverter 30 and then applied to the transistor ₂₄₂ , which turns on the transistor ₂₄₂ , supplying current to the relay coil _C2 and relay RY.
restore to its original state. Even in this case, effects similar to those of the above embodiment can be obtained.

As explained above, according to the present invention, a capacitor is charged with the voltage of a communication line, the charging voltage of this capacitor is used as an operating power source of a relay for forming a communication loop, and the charging voltage of the capacitor is set according to two standards, high and low. When the charging voltage of the capacitor is higher than the higher reference level, the relay is operated to close the call loop, and in this state, the charging voltage of the capacitor is higher than the lower reference level. When the battery becomes small, the relay is restored to its initial state and the call loop is opened, which eliminates the need to charge the battery each time using a battery charger.
Until the charging voltage of the capacitor becomes a stable voltage,
Without operating the relay, unstable operation due to low voltage below the specified value can be reliably prevented.Furthermore, if the relay operates and the capacitor charging voltage falls below the specified value while the call loop is closed, the relay will be initialized. Since the communication loop is opened upon restoration to the normal condition, various excellent effects can be obtained, such as being able to reliably prevent the inconvenience of the communication loop remaining closed in the event of a failure.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the overall configuration of a public telephone to which the present invention is applied, and FIG. 2 is a diagram showing a call loop control circuit according to an embodiment of the present invention.
FIG. 3 is a diagram showing a modification of the same embodiment. 1... Public telephone, 2... Exchange, 11... Call circuit, 12... Power supply circuit, 13... Capacitor, 14... Voltage monitoring circuit, 15... Relay control circuit, RY... Relay, l ₁ ,l ₂ ...Telephone line.

Claims (1)

[Claims] 1. A first contact RYS ₁ that opens and closes the call loop of the public telephone, and a capacitor 13 that stores the voltage of the call line that connects the public telephone and the central office exchange.
and a reference voltage circuit ZD ₁ that creates two reference level voltages, high and low, with respect to the charging voltage of this capacitor.
ZD ₂ , a second contact RYS ₂ for selecting each reference level voltage created by this reference voltage circuit,
a comparator 21 that compares the charging voltage of the capacitor with each of the reference level voltages selected by the second contact, and the output of this comparator determines whether the charging voltage of the capacitor is higher than the reference level voltage of each of the reference level voltages; When the voltage becomes higher than the voltage, the first contact is closed and the second contact is switched to select the lower reference voltage, and when the charging voltage of the capacitor becomes lower than the low reference level voltage. said first
A public telephone set comprising: control means RY, 22, 24 ₁ , 24 ₂ , 25, 30 having a function of opening the contact and switching the second contact to select the higher reference voltage. Call loop control circuit.